Chairs having supports to engage the chest of a user person, such as a dentist, hygienist, surgeon, etc., is known in the art and such chair or seating apparatus are, for example, described in U.S. Pat. Nos. 3,754,787; 4,832,407 and 6,619,747. However, such support chair assemblies still provide disadvantages including freedom of movement of the user person when seated on the chair and performing a work task forwardly of the seating surface. The seat of the chair also needs to provide comfort to the user person particularly when working long hours in a forwardly inclined seated or crouched position. Such chairs also need to provide free rotational movement of the user person when seated on the chair while preventing the chair from overturning and causing injury.
In recent years a study was effected by the ASSTSAS Association and dealing with the risk factors to dentists and dental assistants that work in dental clinics and particularly the problems that such people develop at the musculo-skeleton level due to their work habits. The study revealed that the chairs that these people are using hinder the blood circulation in the legs and cause muscular and spinal back and neck problems due to the fact that the back and neck are inclined forwardly when working on a patient as the back is not properly supported on the chair. When working in such awkward positions for long periods of time all of the tension is directed to the back of the working person which supports the inclined chest and head of the dentist or dental assistant. To counteract the stress on the back, the working person will brace his legs in such a way as to liberate this tension but this has led to the cause of other problems, such as pinching the sciatic nerve. The study effected by the Association of Dental Surgeons and Dentists of the Province of Quebec, Canada (ACDQ) reveals that these people, after working long hours and for several years, develop lower back problems, problems in the neck area and in the shoulders. The more frequent pathologies are tendonitis, bursitis, degeneration of the lumbar disc and the discs in the neck region as well as causing spinal-disc compression and disc hernias, to mention a few. Studies have also shown that the chairs used by dentists often obstruct the dentist's arm movements causing the dentist to assume awkward postures when performing his job function. The study has also shown that the average work life cycle of a dental assistant is about seven (7) years and this is due particularly to all these muscular problems that these people develop due to their work related activities. Also, this type of bad posture causes fatigue and the productivity of the individual is diminished.
The study by ASSTSAS also has resulted in various recommendations concerning the use of proper equipment in an attempt to alleviate all of these muscular and spinal problems. Reference is therefore made to this publication for background art as well as the other studies referred to therein such as studies effected by the American Public Health Association, Herbert 1998, pages 375 to 396. All of the proposed devices have not proven satisfactory to overcome the above-mentioned problems.